The present invention relates to an ultrasonic driving device having a structure for decreasing wear between a stator and a rotary member.
In a known ultrasonic motor using a ring type piezoelectric vibrator, two groups of electrodes are attached to one end of a ring type piezoelectric ceramic, the two groups of electrodes are so positioned that standing waves respectively generated by the two groups of electrodes are shifted every .pi./2 in each position. The parts of the ring type piezoelectric vibrator corresponding to the electrode are alternately polarized in reverse. Also, the two groups of the electrodes are respectively connected to two oscillators for respectively generating alternating current voltages having .pi./2 phase shift from each other. When the alternating current voltages from the two oscillators are respectively applied to the two groups of electrodes, the two standing waves having .pi./2 phase shift from each other are generated on the surfaces of the ring type piezoelectric vibrator and then progressive waves owing to compound of the two standing waves are generated on the surfaces of the ring type piezoelectric vibrator. Therefore, when a slider attaching a rotary member is put on the ring type piezoelectric vibrator and is strongly pressed to the ring type piezoelectric vibrator, the rotary member is rotated by the progressive waves.
In the prior ultrasonic motor, however, the slider is easily worn out because the slider of the rotary member is directly pressed on the piezoelectric vibrator.
There is known an ultrasonic motor comprising a Langevin type vibrator having two ring type piezoelectric vibrators which are put between two metal blocks. In this ultrasonic motor, a twisting joint body is connected to the end of the one metal block by a bolt for fixing the metal blocks and the piezoelectric vibrator and a rotary member is pressed on the twisting joint body by a spring.
In this ultrasonic motor, however, the rotary member is easily worn out because the rotary member is pressed on the twisting joint body.